Laminite, and element comprising substrate manufactured using same

ABSTRACT

The present invention relates to a laminate and a device fabricated using the laminate. The laminate includes a debonding layer including a polyimide resin between a carrier substrate and a flexible substrate. The adhesive strength of the debonding layer to the flexible substrate is changed by a physical stimulus. According to the present invention, the flexible substrate can be easily separated from the carrier substrate without the need for further processing such as laser or light irradiation. Therefore, the use of the laminate facilitates the fabrication of the device having the flexible substrate. The device may be, for example, a flexible display device. In addition, the device can be prevented from deterioration of reliability and occurrence of defects caused by laser or light irradiation. This ensures improved characteristics and high reliability of the device.

TECHNICAL FIELD

The present invention relates to a laminate including a flexiblesubstrate and a carrier substrate from which the flexible substrate iseasily separated even without the need for further processing such aslaser or light irradiation, thus facilitating the fabrication of adevice (for example, a flexible display device) having the flexiblesubstrate. The present invention also relates to a device including asubstrate produced using the laminate.

BACKGROUND ART

The display device market is rapidly changing based on flat paneldisplays (FPDs) that are easy to fabricate over a large area and can bereduced in thickness and weight. Such flat panel displays include liquidcrystal displays (LCDs), organic light emitting displays (OLEDs), andelectrophoresis devices.

In line with recent efforts to further extend the application and use offlat panel displays, particular attention has focused on so-calledflexible display devices in which flexible substrates are applied toflat panel displays. The application of such flexible display devices isparticularly reviewed based on mobile devices such as smart phones andthe application fields thereof are gradually extended.

Processes for the formation and handling of display device structuressuch as thin film transistors (TFTs) on plastic substrates (TOP) areimportant in the fabrication flexible display devices. However, due tothe flexibility of flexible substrates included in flexible displaydevices, many problems still remain in terms of processing when flexibleplastic substrates are directly employed in place of existing glassdevice substrates to form device structures.

Particularly, a thin film glass included in a flexible substrate tendsto be brittle when an impact is applied thereto. Due to this tendency, aprocess for producing a display substrate is carried out in a state inwhich thin film glass is placed on carrier glass. FIG. 1 schematicallyillustrates a process for fabricating a device (e.g., a flexible displaydevice) having a flexible substrate according to the prior art.

Referring to FIG. 1, a sacrificial layer 2 composed of a suitablematerial such as a-silicon is formed on a carrier substrate 1 such as aglass substrate, and a flexible substrate 3 is formed thereon.Thereafter, a device structure such as a thin film transistor is formedon the flexible substrate 3 supported by the carrier substrate 1 inaccordance with a conventional process for the fabrication of a deviceon a glass substrate. Then, laser or light is irradiated onto thecarrier substrate 1 to destroy the sacrificial layer 2 and separate theflexible substrate 3 on which the device structure is formed, completingthe fabrication of a device (for example, a flexible display device)having the flexible substrate 3.

According to the prior art method, however, the laser or lightirradiation affects the device structure, increasing the risk ofdefects. Further, a system for the laser or light irradiation and aseparate process are required, disadvantageously rendering the overalldevice fabrication process complex and markedly increasing thefabrication cost.

Although not illustrated in FIG. 1, it is often necessary to form anadditional adhesive layer between the sacrificial layer 2 composed ofa-Si and the flexible substrate 3 due to insufficient adhesion betweenthe sacrificial layer and the flexible substrate. This makes the overallprocess more complicated and the conditions for laser or lightirradiation more severe, which increases the risk that the reliabilityof the device may be adversely affected.

PRIOR ART DOCUMENTS Patent Documents

(Patent Document 1) PCT International Publication No. WO 2000-066507(published on Nov. 9, 2000)

DISCLOSURE Technical Problem

It is an object of the present invention to provide a laminate includinga flexible substrate and a carrier substrate from which the flexiblesubstrate is easily separated even without the need for furtherprocessing such as laser or light irradiation, thus facilitating thefabrication of a device (for example, a flexible display device) havingthe flexible substrate, and a method for producing the laminate.

It is a further object of the present invention to provide a devicesubstrate produced using the laminate and a method for producing thedevice substrate.

It is another object of the present invention to provide a deviceincluding a substrate produced using the laminate.

Technical Solution

One aspect of the present invention provides a laminate including: acarrier substrate; a debonding layer disposed on at least one surface ofthe carrier substrate and including a polyimide resin; and a flexiblesubstrate disposed on the debonding layer, wherein the adhesive strengthof the debonding layer to the flexible substrate changes when a physicalstimulus causing no chemical changes in the debonding layer is appliedto the laminate.

The physical stimulus may reduce the adhesive strength of the debondinglayer to the flexible substrate. When the adhesive strengths of thedebonding layer to the flexible substrate before and after the physicalstimulus is applied are defined as A1 and A2, respectively, the ratioA2/A1 may be from 0.001 to 0.5.

The debonding layer may have a peel strength not greater than 0.3 N/cmfrom the flexible substrate after the physical stimulus is applied.

The debonding layer may have an adhesive strength of at least 1 N/cm tothe flexible substrate before the physical stimulus is applied.

The physical stimulus may be applied to the debonding layer such thatthe cross-sections of the laminate are exposed.

The polyimide resin may have a similarity score not greater than 0.5, ascalculated by Equation 1:

Similarity score=α_(FIT)(k ₁ ×Ls _(dianhydride,i) +k ₂ ×Ls_(diamine,j))^(k) ₀   [Equation 1]

where

Ls_(dianhydride,i)=Exp[−k₃×Coeff_(i)]×V_(i) ^(y) ₀

Ls_(diamine,j)=Exp[−k₄×Coeff_(j)]×V_(j) ^(y) ₀

k₀=2.00,

y₀=−1.00,

k₁=206.67,

k₂=124.78,

k₃=3.20,

k₄=5.90,

Coeff_(i) and Coeff_(j) are molecular asphericities calculated from thestructures of dianhydride i and diamine j as monomers of the polyimide,respectively, using ADRIANA.Code (Molecular Networks GmbH),

V_(i) and V_(j) are McGowan volumes calculated from the structures ofdianhydride i and diamine j as the monomers, respectively, usingADRIANA.Code (Molecular Networks GmbH), and

α_(FIT) is 1.0 if exp(−4.0×|Coeff_(i)−Coeff_(j)|)+0.08<0.90 and is aconstant from 0.1 to 0.95 if exp(−4.0×Coeff_(i)−Coeff_(j)|)+0.08≧0.90.

The polyimide resin for the debonding layer of the laminate may have animidization degree of 60% to 99% when the imidization degree is definedas the percentage of the integrated intensity of the CN bands observedat 1350 to 1400 cm⁻¹ or 1550 to 1650 cm⁻¹ in the IR spectrum after acomposition including a polyamic acid resin is applied and imidized at atemperature of 200° C. or above with respect to the integrated intensity(100%) of the CN bands observed in the same wavelength range after thecomposition is imidized at a temperature of 500° C. or above.

The polyimide resin may have a glass transition temperature of 200° C.or above.

The polyimide resin may be prepared by reacting a tetracarboxylicdianhydride of Formula 1:

wherein A is a tetravalent aromatic organic group of Formula 2a or 2b:

wherein R₁₁ is a C₁-C₄ alkyl or C₁-C₄ haloalkyl group, a is an integerfrom 0 to 3, and b is an integer from 0 to 2,

wherein R₁₂ to R₁₄ are each independently a C₁-C₄ alkyl or C₁-C₄haloalkyl group, c and e are each independently an integer from 0 to 3,d is an integer from 0 to 4, and f is an integer from 0 to 3, with anaromatic diamine compound having a linear structure to prepare apolyamic acid, and curing the polyamic acid at a temperature of 200° C.or above.

The aromatic diamine compound may be represented by Formula 4a or 4b:

wherein R₂₁ is a C₁-C₁₀ alkyl or C₁-C₁₀ haloalkyl group and 1 is aninteger from 0 to 4,

wherein R₂₂ and R₂₃ are each independently a C₁-C₁₀ alkyl or C₁-C₁₀haloalkyl group, X is selected from the group consisting of —O—,—CR₂₄R₂₅—, —C(═O)—, —C(═O)O—, —C(═O)NH—, —S—, —SO—, —SO₂—,—O[CH₂CH₂O]_(q)—, C₆-C₁₈ monocyclic and polycyclic cycloalkylene groups,C₆-C₁₈ monocyclic and polycyclic arylene groups, and combinationsthereof, R₂₄ and R₂₅ are each independently selected from the groupconsisting of a hydrogen atom, C₁-C₁₀ alkyl groups, and C₁-C₁₀ haloalkylgroups, q is an integer of 1 or 2, m and n are each independently aninteger from 0 to 4, and p is an integer of 0 or 1.

The debonding layer may be formed by applying a composition includingthe polyimide resin or a precursor thereof to the carrier substrate andcuring the composition at a temperature of 200° C. or above.

The debonding layer may have a coefficient of thermal expansion nothigher than 30 ppm/° C. at a temperature of 100 to 200° C. and a 1%thermal decomposition temperature (Td1%) of 450° C. or above.

The debonding layer may have a thickness of 0.05 to 5 μm.

The flexible substrate of the laminate may include a structure selectedfrom the group consisting of thin film glass layers, polymer layers, andmultilayer laminates thereof.

The polymer layer of the flexible substrate may include at least onepolymer resin selected from the group consisting of polyethersulfone,polyethylene naphthalate, polyethylene terephthalate, polycarbonate,polyimide, polyether imide, polyamide imide, polyester, polyether amideimide, polyester amide imide, and polyarylate.

The polymer layer may include a polyimide resin having an imidizationdegree of 50 to 99% and a glass transition temperature of 200° C. orabove.

A further aspect of the present invention provides a method forproducing a laminate, including: forming a debonding layer including apolyimide resin on at least one surface of a carrier substrate; andforming a flexible substrate on the debonding layer, wherein thedebonding layer may be formed by applying a composition including thepolyimide resin or a precursor thereof to the carrier substrate andcuring the composition at a temperature of 200° C. or above.

The flexible substrate may be formed by a method selected from the groupconsisting of a method including disposing a glass thin film layer onthe debonding layer and heat treating the glass thin film layer at atemperature of 20 to 300° C., a method including applying a compositionincluding a polymer or a precursor thereof and curing the composition,and a combination thereof.

The method for producing a laminate may further include heat treatingthe debonding layer at a temperature of 300° C. or above for 1 to 30minutes after the step of forming the debonding layer.

Another aspect of the present invention provides a method for producinga device substrate, including: forming a debonding layer including apolyimide resin on at least one surface of a carrier substrate; forminga flexible substrate on the debonding layer to produce a laminate;applying a physical stimulus to the laminate without causing chemicalchanges in the debonding layer; and separating the flexible substratefrom the carrier substrate on which the debonding layer is formed,wherein the debonding layer is formed by applying a compositionincluding the polyimide resin or a precursor thereof to the carriersubstrate and curing the composition at a temperature of 200° C. orabove.

The physical stimulus is applied such that the cross-sections of thelaminate are exposed.

Yet another aspect of the present invention provides a device fabricatedby a method including: producing a laminate including a carriersubstrate, a debonding layer, and a flexible substrate; forming a devicestructure on the flexible substrate of the laminate; and applying aphysical stimulus to the laminate on which the device structure isformed, without causing chemical changes in the debonding layer, andseparating the flexible substrate on which the device structure isformed, from the debonding layer of the laminate.

The device may be selected from the group consisting of solar cells,organic light emitting diode lighting devices, semiconductor devices,and display devices.

The display devices may be flexible organic electroluminescent devices.

Details of other embodiments according to various aspects of theinvention are included in the following description.

Advantageous Effects

In the laminate of the present invention, the flexible substrate can beeasily separated from the carrier substrate by the application of arelatively small physical stimulus such as cutting, eliminating the needfor laser or light irradiation. Therefore, the use of the laminatefacilitates the fabrication of a device (for example, a flexible displaydevice) including the flexible substrate.

According to the present invention, since there is no need foradditional processing such as laser or light irradiation, thefabrication process of the device can be simplified and the fabricationcost can be greatly lowered. In addition, the device can be preventedfrom deterioration of reliability and occurrence of defects caused bylaser or light irradiation. This ensures excellent characteristics ofthe device.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a conventional process forfabricating a device including a flexible substrate,

FIG. 2 a is a cross-sectional view schematically illustrating thestructure of a laminate according to one embodiment of the presentinvention, and FIG. 2 b is a cross-sectional view schematicallyillustrating the structure of a laminate according to a furtherembodiment of the present invention,

FIGS. 3 a and 3 b are schematic views illustrating processes for theproduction of a device substrate and the fabrication of a display deviceusing a laminate according to another embodiment of the presentinvention, respectively,

FIG. 4 is a graph showing changes in the dimension of debonding layersincluding different first polyimide resins with varying temperatures inTest Example 1,

FIG. 5 is a graph showing changes in the peel strength of debondinglayers with varying thicknesses of flexible substrates in Test Example3, and

FIG. 6 is a graph showing changes in the peel strength of debondinglayers with increasing number of subsequent heat treatments after curingof the debonding layers in Test Example 5.

MODE FOR INVENTION

As the present invention allows for various changes and numerousembodiments, particular embodiments will be illustrated in drawings anddescribed in detail in the written description. However, this is notintended to limit the present invention to particular modes of practice,and it is to be appreciated that all changes, equivalents, andsubstitutes that do not depart from the spirit and technical scope ofthe present invention are encompassed in the present invention. In thedescription of the present invention, detailed explanations of relatedart are omitted when it is deemed that they may unnecessarily obscurethe essence of the present invention.

It will be understood that when an element such as a layer, membrane,film or substrate is referred to as being “above” or “on” anotherelement, it can be directly on the other element or one or moreintervening elements may also be present. It will also be understoodthat when an element such as a layer, membrane, film or substrate isreferred to as being “under” another element, it can be directly underthe other element or one or more intervening elements may also bepresent.

Unless otherwise mentioned, the term ‘physical stimulus’ used herein isintended to include mechanical stimuli such as peeling, cutting,friction, tension and compression causing no chemical changes, and itrefers to a stimulus by which the cross-sections of a laminate can beexposed regardless of what means or mode is employed. In some cases, thephysical stimulus may have a strength of 0 to 0.1 N per unit area. Thatis, the application of the physical stimulus means that thecross-sections of a laminate are exposed regardless of what means isused. Preferably, the physical stimulus is applied in such a manner thattwo or more cross-sections of a laminate forming the end portions of aflexible substrate are exposed at predetermined intervals.

The present invention provides a laminate including: a carriersubstrate; a debonding layer disposed on at least one surface of thecarrier substrate and including a polyimide resin; and a flexiblesubstrate disposed on the debonding layer, wherein the adhesivestrengths of the debonding layer to the flexible substrate are differentbefore and after the application of a physical stimulus causing nochemical change in the debonding layer.

As used herein, the term ‘adhesive strength’ refers to the adhesivestrength of the debonding layer to the flexible substrate before thephysical stimulus is applied, and the term ‘peel strength’ refers to theadhesive strength of the debonding layer to the flexible substrate afterthe physical stimulus is applied. The term ‘adhesive strength’ isinterchangeably used with the term ‘peel strength’.

The present invention also provides a laminate including: a carriersubstrate; a debonding layer disposed on at least one surface of thecarrier substrate and including a polyimide resin; and a flexiblesubstrate disposed on the debonding layer, wherein when the adhesivestrengths of the debonding layer to the flexible substrate before andafter a physical stimulus is applied are defined as A1 and A2,respectively, the ratio A2/A1 is from 0.001 to 0.5.

The present invention also provides a method for producing a laminate,including: forming a debonding layer including a polyimide resin on atleast one surface of a carrier substrate; and forming a flexiblesubstrate on the debonding layer, wherein the debonding layer is formedby applying a composition including the polyimide resin or a precursorthereof to the carrier substrate and curing the composition at atemperature of 200° C. or above.

The present invention also provides a method for producing a devicesubstrate, including: forming a debonding layer including a polyimideresin on at least one surface of a carrier substrate; forming a flexiblesubstrate on the debonding layer; and applying a physical stimulus tothe flexible substrate to separate the flexible substrate from thedebonding layer formed on the carrier substrate, wherein the debondinglayer is formed by applying a composition including the polyimide resinor a precursor thereof to the carrier substrate and curing thecomposition at a temperature of 200° C. or above.

The present invention also provides a device substrate produced by themethod.

The present invention also provides a device including the devicesubstrate.

A more detailed description will now be given of a laminate, a methodfor producing the laminate, a device substrate produced using thelaminate, a method for producing the device substrate, a deviceincluding the device substrate, and a method for fabricating the deviceaccording to embodiments of the present invention.

According to one embodiment of the present invention, a laminate isprovided which includes: a carrier substrate; a debonding layer disposedon at least one surface of the carrier substrate and including apolyimide resin; and a flexible substrate disposed on the debondinglayer, wherein the adhesive strengths of the debonding layer to theflexible substrate are different before and after a physical stimulus isapplied.

Specifically, the physical stimulus reduces the adhesive strength of thedebonding layer to the flexible substrate. More specifically, thedebonding layer has an adhesive strength of at least 1 N/cm to theflexible substrate before the physical stimulus is applied but has apeel strength not greater than 0.3 N/cm from the flexible substrateafter the physical stimulus is applied. The physical stimulus is appliedsuch that the cross-sections of the laminate are exposed and may have astrength not greater than 0.1 N. Specific examples of methods forapplying the physical stimulus to expose the cross-sections of thelaminate include, but are not limited to, cutting, laser cutting, anddiamond scribing.

As a result of experiments conducted by the present inventors, it wasfound that when the debonding layer including a polyimide resin withparticular characteristics is disposed between the carrier substrate andthe flexible substrate, which is to be applied as a substrate for adevice (for example, a flexible display device), the application of asimple physical stimulus makes the flexible substrate easily separablefrom the debonding layer without the need for laser or lightirradiation, facilitating the fabrication of the device having theflexible substrate. Such functions and effects are thought to beattributed to the characteristics of the polyimide resin, which will bedescribed below.

FIG. 2 a is a cross-sectional view schematically illustrating thestructure of a laminate according to one embodiment of the presentinvention. The structure of FIG. 2 a is merely for illustrative purposesand the invention is not limited thereto.

Referring to FIG. 2 a, the laminate 10 of the present invention includesa carrier substrate 11, a debonding layer 12 disposed on at least onesurface of the carrier substrate and including a polyimide resin, and aflexible substrate 13 disposed on the debonding layer.

The carrier substrate 11 may be any one that is used to support theflexible substrate 13 such that a device can be easily fabricated on thelaminate 10. Specific examples of suitable carrier substrates includeglass substrates, metal substrates such as stainless steel substrates,and multilayer structures thereof. Particularly preferred is a glasssubstrate that is most easily applicable to the fabrication of a device.

The carrier substrate 11 may be pretreated by etching, for example,corona treatment under an ozone atmosphere, flame treatment, sputtering,UV irradiation or e-beam irradiation. This pretreatment increases theadhesion of the carrier substrate to the debonding layer.

The thickness and size of the carrier substrate 11 may be suitablyselected depending on the kind of a device to which the laminate is tobe applied. The thickness of the carrier substrate 11 is preferably inthe range of 0.1 to 50 mm taking into consideration the transparency ofthe substrate. Within this range, the mechanical strength of the carriersubstrate 11 is sufficiently high to support the flexible substrate.

The debonding layer 12 including a polyimide resin is disposed on atleast one surface of the carrier substrate 11.

The imidization degree of the polyimide resin included in the debondinglayer 12 is controlled to an appropriate range, which will be describedbelow. The debonding layer exhibits an adhesive strength above apredetermined level so as to appropriately fix and support the flexiblesubstrate 13 in a subsequent process for fabricating a device includingforming a device structure on the flexible substrate 13. However, afterthe device fabrication process is completed, the adhesive strength ofthe debonding layer to the flexible substrate 13 can be reduced by asimple physical stimulus such as cutting without laser or lightirradiation, and hence, the debonding layer 12 can be easily separatedfrom the flexible substrate 13.

Specifically, when the adhesive strengths of the debonding layer 12 tothe flexible substrate 13 before and after a physical stimulus isapplied are defined as A1 and A2, respectively, the ratio A2/A1 is from0.001 to 0.5, preferably from 0.001 to 0.1. The debonding layer 12 canbe easily separated from the flexible substrate 13 by a simple physicalstimulus such as cutting without laser or light irradiation.

More specifically, the debonding layer 12 exhibits an adhesive strengthof at least about 1 N/cm, at least about 2N/cm, or about 3 to about 5N/cm to the flexible substrate 13 before the application of the physicalstimulus but can exhibit a peel strength of about 0.3 N/cm or less, forexample, about 0.2 N/cm or less, about 0.1 N/cm or less, or about 0.001to 0.05 N/cm after the application of the physical stimulus.

The peel strength of the debonding layer 12 can be measured under theconditions shown in Table 1.

TABLE 1 Conditions for peel Film width 10 strength (mm) measurement Filmlength 100  (mm) Rate 50 (mm/min) Tester Texture Analyzer (TA.XT plus,Stable micro systems)

Specifically, the peel strength can be determined by the followingprocedure. First, a debonding layer and a flexible substrate aresequentially formed on a glass substrate to prepare a laminate sample. Aphysical stimulus is applied to cut the laminate sample into arectangular shape having a width of 10 mm. The force required to peelthe ends of the flexible substrate from the debonding layer is measuredusing the tester under the conditions shown in Table 1. This force isdefined as the peel strength of the debonding layer.

The adhesive strength can be determined by the following procedure.First, a debonding layer and a flexible substrate are sequentiallyformed on a glass substrate to prepare a laminate sample having a widthof 100 mm. The ends of the flexible substrate of the sample are attachedwith tapes, each having a width of 10 mm. The force required to peel theends of the tapes from the debonding layer is measured. This force isdefined as the adhesive strength of the debonding layer. A tester andconditions for measuring the force may be the same as those for the peelstrength measurement shown in Table 1.

The desired adhesive strength and peel strength of the debonding layer12 can be achieved by the imidization degree of the polyimide resinincluded in the debonding layer. The imidization degree can becontrolled by various factors, for example, the kind and content ofmonomers for the polyimide resin and the imidization conditions (such asheat treatment temperature and time).

As an example, the polyimide resin included in the debonding layer 12may have an imidization degree of about 60% to about 99%, about 70% to98% or about 75% to 96%. Within this range, the debonding layer 12 canmeet the requirements in terms of adhesive strength and peel strength,and hence, the flexible substrate 13 can be easily separated from thedebonding layer 12 even when a physical stimulus is applied without theneed for laser or light irradiation. The imidization degree of thepolyimide resin can be defined as the percentage of the integratedintensity of the CN bands observed at 1350 to 1400 cm⁻¹ or 1550 to 1650cm⁻¹ in the IR spectrum after a composition including a polyimideprecursor, for example, a polyamic acid resin, is applied and imidizedat a temperature of 200° C. or above with respect to the integratedintensity (100%) of the CN bands observed in the same wavelength rangeafter the composition is imidized at a temperature of 500° C. or above.

The imidization degree range of the polyimide resin can be achieved bycontrolling the temperature condition for curing the polyamic acidresin.

As a result of experiments conducted by the present inventors, it wasconfirmed that the curing temperature conditions for the preparation ofthe polyimide resin, the imidization degree of the polyimide resin, andthe peel strength of the polyimide resin layer can satisfy therelationships shown in Table 2.

TABLE 2 Curing temperature (° C.) 150 200 250 300 350 500 Imidizationdegree (%) 10.36 49.21 79.34 92.78 95.69 100 Peel strength (N/cm) 2.82.8 0.03 0.016 0.03 0.35

As shown in Table 2, when the debonding layer is formed by applying acomposition including a polyamic acid resin as a precursor of thepolyimide resin to the carrier substrate and curing the composition at atemperature of about 200° C. or above or 250° C. to 500° C., thedebonding layer has a peel strength not greater than about 0.3 N/cm andthe polyimide resin included in the debonding layer has an imidizationdegree of about 60% to about 99%, about 70% to about 98%, or about 75%to about 96%. The use of the laminate according to this embodimentmarkedly simplifies a process for the fabrication of a device (such as aflexible display device) including the flexible substrate, which hasalready been described above.

The polyimide resin prepared under the control of the curing temperaturemay have a glass transition temperature of at least about 200° C., atleast about 300° C., or about 350° C. to about 500° C. and adecomposition temperature (Td) of at least 400° C. or 400° C. to 600° C.Due to good heat resistance of the polyimide resin, the debonding layeris highly resistant to high temperature during processing for thefabrication of a device and can be prevented from warpage in the courseof fabricating a device on the laminate. In addition, the debondinglayer can prevent the reliability of a device from deteriorating. As aresult, the use of the debonding layer enables the fabrication of adevice with improved characteristics and high reliability. Specifically,the debonding layer of the laminate according to this embodiment mayhave a coefficient of thermal expansion (CTE) not higher than about 30ppm/° C., not higher than about 25 ppm/° C., or from about 1 to about 17ppm/° C. at a temperature of 100 to 200° C. and a 1% thermaldecomposition temperature (Td1%) of 450° C. or above.

The debonding layer 12 meeting the requirements in terms of structuraland physical properties is completely peeled from the flexible substrate13 and thus has no influence on the transparency and optical propertiesof a device substrate.

The present inventors have found that the adhesive strength of thedebonding layer varies depending on the kinds of a dianhydride and adiamine for the polyimide constituting the debonding layer. Based onthis finding, the present inventors suggest a method for quantitativelyevaluating the adhesive strength of the debonding layer. Specifically,the present inventors have developed a monomer combination basedsimilarity score. A higher similarity score represents anonlinear/nonplanar structure having a higher structural similarity to asphere. Meanwhile, a lower similarity score represents a linear/planarstructure having a lower structural similarity to a sphere. In thepresent invention, the similarity score is preferably not greater than0.5.

The similarity is calculated by Equation 1.

Similarity score=α_(FIT)(k ₁ ×Ls _(Dianhydride,i) +k ₂ ×Ls_(Diamine,j))k ₀   [Equation 1]

where

Ls_(Dianhydride,i)=Exp[−k₃×Coeff_(i)]×V_(i) ^(y) ₀

Ls_(Diamine,j)=Exp[−k₄×Coeff_(i)]×V_(j) ^(y) ₀

k₀=2.00,

y₀=−1.00,

k₁=206.67,

k₂=124.78,

k₃=3.20,

k₄=5.90,

Coeff_(i) and Coeff_(j) are molecular asphericities calculated from thestructures of dianhydride i and diamine j as monomers of the polyimide,respectively, using ADRIANA.Code (Molecular Networks GmbH),

V_(i) and V_(j) are McGowan volumes calculated from the structures ofdianhydride i and diamine j as the monomers, respectively, usingADRIANA.Code (Molecular Networks GmbH), and

α_(FIT) is 1.0 if exp(−4.0×Coeff_(i)−Coeff_(j)|)+0.08<0.90 and is aconstant from 0.1 to 0.95 if exp(−4.0×|Coeff_(i)−Coeff_(j))+0.08≧0.90.

In Equation 1, if exp(−4.0×|Coeff_(i)−Coeff_(j))+0.08≧0.90, α_(FIT) is aconstant from 0.1 to 0.95, preferably from 0.2 to 0.5, most preferably0.33.

ADRIANA.Code is a program developed by Molecular Networks GmbH, Germanyand is mainly used to calculate the inherent physical, chemical andelectrical properties of molecules. When the structural information ofmolecules is input to the program, the molecular asphericities andMcGowan volumes can be calculated.

A polyamic acid resin as a precursor of the polyimide resin may beprepared by polymerizing a tetracarboxylic dianhydride compound and adiamine compound as monomers. The polyimide resin may be prepared byimidization of the polyamic acid resin.

Specific examples of tetracarboxylic dianhydride compounds suitable asmonomers include pyromellitic dianhydride (PMDA),3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA),meso-buthane-1,2,3,4-tetracarboxylic dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 2,3,3′,4′-diphenylethertetracarboxylic dianhydride, (ODPA), 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA),4,4′-(hexafluoroisopropylidene)diphthalic anhydride,3,3′,4,4′-biphenyltetracarboxylic dianhydride (S-BPDA),1,2,3,4-cyclobutane tetracarboxylic dianhydride,1,2-dimethyl-1,2,3,4-cyclobutane tetracarboxylic dianhydride,1,2,3,4-tetramethyl-1,2,3,4-cyclobutane tetracarboxylic dianhydride,1,2,3,4-cyclopentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride,3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic dianhydride,5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylicdianhydride, 2,3,5-tricarboxy-2-cyclopentane acetic dianhydride,bicyclo[2.2.2]octo-7-en-2,3,5,6-tetracarboxylic dianhydride,2,3,4,5-tetrahydrofuran tetracarboxylic dianhydride,3,5,6-tricarboxy-2-norbornane acetic dianhydride, and derivativesthereof. It should be understood that other various tetracarboxylicdianhydrides may also be used.

Specific examples of diamine compounds suitable as monomers include:aromatic diamines, such as p-phenylenediamine (PDA), m-phenylenediamine(m-PDA), 2,4,6-trimethyl-1,3-phenylenediamine,2,3,5,6-tetramethyl-1,4-phenylenediamine, 4,4′-diaminodiphenyl ether,3,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether,4,4′-diaminodiphenyl sulfide, 4,4′-diaminodiphenylmethane,3,4′-diaminodiphenylmethane, 3,3′-diaminodiphenylmethane,4,4′-methylene-bis(2-methylaniline),4,4′-methylene-bis(2,6-dimethylaniline),4,4′-methylene-bis(2,6-diethylaniline),4,4′-methylene-bis(2-isopropyl-6-methylaniline),4,4′-methylene-bis(2,6-diisopropylaniline), 4,4′-diaminodiphenylsulfone,3,3′-diaminodiphenylsulfone, benzidine, o-tolidine, m-tolidine,3,3′,5,5′-tetramethylbenzidine, 2,2′-bis(trifluoromethyl)benzidine,1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,1,3-bis(3-aminophenoxy)benzene, bis[4-(4-aminophenoxy)phenyl]sulfone,bis[4-(3-aminophenoxy)phenyl]sulfone,2,2-bis[4-(4-aminophenoxy)phenyl]propane,2,2-bis[4-(3-aminophenoxy)phenyl]propane,2,2-bis[4-(4-aminophenoxy)phenyl]propane (6HMDA),2,2′-bis(trifluoromethyl)benzidine (TFMB),3,3′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (3,3′-TFDB),4,4′-bis(3-aminophenoxy)diphenylsulfone (DBSDA),bis(3-aminophenyl)sulfone (3DDS), bis(4-aminophenyl)sulfone (4DDS),1,3-bis(3-aminophenoxy)benzene (APB-133), 1,4-bis(4-aminophenoxy)benzene(APB-134), 2,2′-bis[3(3-aminophenoxy)phenyl]hexafluoropropane (3-BDAF),2,2′-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (4-BDAF),2,2′-bis(3-aminophenyl)hexafluoropropane (3,3′-6F),2,2′-bis(4-aminophenyl)hexafluoropropane (4,4′-6F), and4,4′-oxydianiline (ODA); and aliphatic diamines, such as1,6-hexanediamine, 1,4-cyclohexanediamine, 1,3-cyclohexanediamine,1,4-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane,4,4′-diaminodicyclohexylmethane,4,4′-diamino-3,3′-dimethyldicyclohexylmethane,4,4′-diamino-3,3′-dimethyldicyclohexylmethane,1,2-bis-(2-aminoethoxy)ethane, bis(3-aminopropyl)ether,1,4-bis(3-aminopropyl)piperazine,3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro[5.5]-undecane, and1,3-bis(3-aminopropyl)tetramethyldisiloxane.

There is no particular restriction on the kinds of the tetracarboxylicdianhydride and the diamine compound, but it is important for the aciddianhydride to have no linker structure between aromatic rings in orderto more appropriately meet the requirements of the debonding layer interms of physical properties, for example, low CTE range and peelstrength described above. The tetracarboxylic dianhydride is preferablyan aromatic tetracarboxylic dianhydride of Formula 1:

wherein A is a tetravalent aromatic organic group derived from an aciddianhydride, specifically a tetravalent aromatic organic group ofFormula 2a or 2b:

wherein R₁₁ is a C₁-C₄ alkyl (for example, methyl, ethyl or propyl) orC₁-C₄ haloalkyl (for example, fluoromethyl, bromomethyl, chloromethyl ortrifluoromethyl) group, a is an integer from 0 to 3, and b is an integerfrom 0 to 2, preferably 0,

wherein R₁₂ to R₁₄ are each independently a C₁-C₄ alkyl (for example,methyl, ethyl or propyl) or C₁-C₄ haloalkyl (for example, fluoromethyl,bromomethyl, chloromethyl or trifluoromethyl) group, c and e are eachindependently an integer from 0 to 3, preferably 0, d is an integer from0 to 4, preferably 0, and f is an integer from 0 to 3.

Particularly, the tetracarboxylic dianhydride is more preferablypyromellitic dianhydride (PMDA) of Formula 3a or3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) of Formula 3b:

In the compound of Formula 3b, the structure is linear and the twoaromatic rings are directly connected without a linker structure.

As the packing density of the debonding layer 12 increases, theintermolecular space decreases and it is thus difficult for themolecules to interpenetrate, resulting in low bonding strength. As aconsequence, the adhesive strength of the debonding layer 12 to theoverlying flexible substrate 13 is reduced and the peel strength of theflexible substrate from the laminate is also reduced. The packingdensity can be represented by CTE. The higher the packing density, thelower the CTE value, and vice versa. Accordingly, it is preferred thatthe diamine compound is an aromatic diamine compound having a linearstructure, specifically, an aromatic diamine compound of Formula 4a or4b:

wherein R₂₁ is a C₁-C₁₀ alkyl (for example, methyl, ethyl or propyl) orC₁-C₄ haloalkyl (for example, fluoromethyl, bromomethyl, chloromethyl ortrifluoromethyl) group and 1 is an integer from 0 to 4, preferably 0,

wherein R₂₂ and R₂₃ are each independently a C₁-C₁₀ alkyl (for example,methyl, ethyl or propyl) or C₁-C₄ haloalkyl (for example, fluoromethyl,bromomethyl, chloromethyl or trifluoromethyl) group, X is selected fromthe group consisting of —O—, —CR₂₄R₂₅—, —C(═O)—, —C(═O)O—, —C(═O)NH—,—S—, —SO—, —SO₂—, —O[CH₂CH₂O]_(q)—, C₆-C₁₈ monocyclic and polycycliccycloalkylene (for example, cyclohexylene and norbornene) groups, C₆-C₁₈monocyclic and polycyclic arylene (for example, phenylene andnaphthalene) groups, and combinations thereof, R₂₄ and R₂₅ are eachindependently selected from the group consisting of a hydrogen atom,C₁-C₁₀ alkyl (for example, methyl, ethyl and propyl) groups, and C₁-C₁₀haloalkyl (for example, fluoromethyl, bromomethyl, chloromethyl andtrifluoromethyl) groups, q is an integer of 1 or 2, m and n are eachindependently an integer from 0 to 4, preferably 0, and p is an integerof 0 or 1, preferably 0.

The use of the aromatic diamine compound more appropriately meets therequirements of the debonding layer in terms of physical properties.

Examples of preferred aromatic diamine compounds includep-phenylenediamine (PDA), benzidine (BZD), m-tolidine, and2,2′-bis(trifluoromethyl)benzidine (TFMB).

These monomers are polymerized in a polar organic solvent to prepare thedesired polyamic acid resin. The polyamic acid resin is subjected toimidization at the curing temperature described above in the presence orabsence of an imidization catalyst such as an amine catalyst to preparethe polyimide resin. The debonding layer including the polyimide resincan meet the requirements in terms of physical properties. Conditionsother than the curing temperature for the preparation of the polyamicacid resin or the polyimide resin can be controlled by suitable methodswell known to those skilled in the art, and a further explanationthereof is thus omitted.

The debonding layer 12 may have a thickness of 0.05 to 5 μm, 0.05 to 4μm, 0.05 to 3 μm, 0.05 to 2 μm, or 0.05 to 1 μm. As the debonding layerdecreases in thickness, its adhesive strength to the carrier substrateincreases. However, an excessively small thickness of the debondinglayer leads to an increase in the adhesive strength of the debondinglayer to the flexible substrate, resulting in poor detachability of thedebonding layer from the flexible substrate. Within the thickness rangedefined above, high adhesive strength of the debonding layer to thecarrier substrate and good detachability of the debonding layer from theflexible substrate are ensured.

In the laminate, the flexible substrate 13 is disposed on the debondinglayer 12.

The flexible substrate 13 may include a structure selected from thegroup consisting of a thin film glass layer 13 a, a polymer layer 13 b,and a multilayer laminate thereof.

Any glass material that is used in general display devices may be usedas a material for the thin film glass layer 13 a of the flexiblesubstrate 13. Specific examples of materials suitable for the thin filmglass layer 13 a include soda lime glass, neutral borosilicate glass,and non-alkali glass. The material for the thin film glass layer issuitably selected depending on a device where it is to be applied.Non-alkali glass is preferably applied to a device requiring a lowcoefficient of thermal shrinkage, and soda lime glass with high visiblelight transmittance is preferably applied to a device requiring hightransparency.

More preferably, the above materials are mixed in appropriate amountssuch that the thin film glass layer 13 a has an average coefficient ofthermal expansion at 25 to 200° C. (hereinafter referred to simply as an“average coefficient of thermal expansion”) of 0 to 200×10⁻⁷/° C.,preferably 0 to 50×10⁻⁷/° C., and a visible light transmittance of atleast 90%. When the average coefficient of thermal expansion of the thinfilm glass layer 13 a is in the range defined above, device elementsformed on a heated substrate of a device can be prevented fromdislocation upon cooling.

The thin film glass layer 13 a may be formed in accordance with anysuitable method known in the art. Specifically, the thin film glasslayer 13 a can be formed by mixing glass raw materials, melting themixture, shaping the molten mixture into a plate, and cutting the plateto a suitable size. The shaping may be performed by a float process, aslot down-draw process, an overflow process, a down-draw process, afusion process, a redraw process, or a roll-out process.

The dimensions (for example, thickness and size) of the thin film glasslayer 13 a may be suitably selected depending on the kind of a device towhich the laminate is to be applied. Preferably, the thin film glasslayer 13 a has a thickness in the range of 10 to 200 μm taking intoconsideration the transparency of a device substrate. Within this range,the thin film glass layer 13 a can exhibit high flexibility togetherwith proper mechanical strength.

The polymer layer 13 b may be formed on or under the thin film glasslayer 13 a. Alternatively, polymer layers 13 b may be formed on bothsurfaces of the thin film glass layer 13 a. The thin film glass layer 13a may be pretreated by etching, for example, corona treatment under anozone atmosphere, flame treatment, sputtering, UV irradiation or e-beamirradiation. This pretreatment increases the adhesion of the thin filmglass layer 13 a to the polymer layer 13 b.

A material for the polymer layer 13 b of the flexible substrate 13 isnot particularly limited and may be any polymer that is known to beapplicable to general substrates of flexible devices. Specifically, thepolymer layer 13 b may include at least one polymer resin selected fromthe group consisting of polyethersulfone, polyethylene naphthalate,polyethylene terephthalate, polycarbonate, polyimide, polyether imide,polyamideimide, polyester, polyether amide imide, polyester amide imide,and polyarylate.

A polyimide resin is particularly preferred as the material for thepolymer layer 13 b. Specifically, the polyimide resin may have animidization degree of about 50 to about 99% or about 70 to about 95%, aglass transition temperature (Tg) of at least about 200° C., at leastabout 300° C. or about 350 to 500° C., and a decomposition temperature(Td) of at least 400° C. or 400 to 600° C. Such good heat resistance ofthe polyimide resin eliminates the risk that the polymer layer 13 b maybe deformed during subsequent heating for the production of the laminateor a device substrate, and leads to improvements in the heat resistanceof the substrate and a device. Specifically, the polymer layer 13 b mayhave a coefficient of thermal expansion (CTE) of about 60 ppm/° C. orless, about 50 ppm/° C. or less, about 40 ppm/° C. or less, or about 1to 30 ppm/° C. at 100 to 200° C., and a 1% thermal decompositiontemperature (Td1%) of 450° C. or more or 470° C. or more.

The polyimide resin included in the polymer layer 13 b may also beprepared by polymerization of an acid dianhydride and a diamine compoundas monomers to prepare a polyamic acid resin and curing the polyamicacid resin. The polymer layer 13 b may be formed by drying a compositionin the form of a solution including the polyimide resin. The aciddianhydride and the diamine compound are the same as those described inthe preparation of the polyimide resin for the formation of thedebonding layer.

For the preparation of the polyimide resin meeting the requirements interms of physical properties, it is preferred to appropriately controlthe kinds and ratio of the monomers for the polyimide resin and theimidization conditions. As an example, it is preferred to appropriatelycontrol the ratio of an acid dianhydride and a diamine duringpolymerization in order to meet the requirements of the polymer layer 13b in terms of physical properties. Specifically, it would be desirablethat to use the diamine in an amount of 0.8 to 1.2 moles or 0.9 to 1.1moles per mole of the tetracarboxylic dianhydride.

The polymer layer 13 b having the above physical properties may have athickness of 0.5 to 50 μm, 1 to 50 μm, 2 to 50 μm, 3 to 50 μm, or 3 to30 μm. Particularly, when the polymer layer 13 b is in contact with thedebonding layer, it is preferable that the polymer layer 13 b has anoptimum thickness. For example, the thickness of the polymer layer 13 bmay be 10 to 500 times, 20 to 400 times, 30 to 300 times, or 50 to 200times larger than that of the debonding layer.

According to one embodiment, the flexible substrate 13 of the laminatemay include the thin film glass layer 13 a and the polymer layer 13 b,each of which is in the form of a monolayer. Alternatively, each of thethin film glass layer 13 a and the polymer layer 13 b may be formed inplurality. That is, the flexible substrate 13 may include a multilayerstructure in which two or more layers of thin film glass layers 13 a andtwo or more layers of polymer layers 13 b are laminated. The laminate 10according to this embodiment of the present invention includes theflexible substrate having a bilayer structure in which the polymer layer13 b is laminated under the thin film glass layer 13 a, as illustratedin FIG. 2 a. A further embodiment of the present invention provides alaminate 20 illustrated in FIG. 2 b. The laminate 20 includes a flexiblesubstrate 23 having a trilayer structure in which polymer layers 23 band 23 c are formed on both surfaces of a thin film glass layer 23 a.However, the laminate of the present invention is not limited to thismultilayer structure. In the flexible substrate having a multilayerstructure, the polymer layer 23 c formed on the thin film glass layer 23a may serve as a protective film for the thin film glass layer.

The laminate 10 having the above structure may be produced in accordancewith a method including the following steps: forming a debonding layer12 including a polyimide resin on at least one surface of a carriersubstrate 11 (step 1); and forming a flexible substrate 13 on thedebonding layer 12 (step 2).

Hereinafter, the individual steps will be explained in detail. In step1, a debonding layer 12 is formed on a carrier substrate 11.

The carrier substrate 11 is the same as that described above. Beforeformation of the debonding layer 12, the carrier substrate 11 may bepretreated by etching, for example, corona treatment under an ozoneatmosphere, flame treatment, sputtering, UV irradiation or e-beamirradiation. This pretreatment increases the adhesion of the carriersubstrate to the debonding layer.

The debonding layer 12 may be formed by applying a composition includinga polyimide resin or a polyamic acid resin as a precursor of thepolyimide resin to the carrier substrate 11 and curing the compositionat a temperature of 200° C. or above. During the curing, imidization ofthe polyamic acid resin proceeds.

The polyimide resin and the polyamic acid resin included in thecomposition for the formation of the debonding layer are the same asthose explained above.

The composition for the formation of the debonding layer may furtherinclude at least one additive selected from binders, solvents,cross-linkers, initiators, dispersants, plasticizers, viscositymodifiers, UV absorbers, photosensitive monomers, and sensitizers, whichare commonly used in polyimide resin layers.

The composition may be applied by any suitable technique known in theart. Specific examples of techniques suitable for the application of thecomposition include spin coating, dip coating, and bar coating. Casting,rolling or spray coating may be suitably used for a continuous process.

Before the curing, drying may be further performed to remove organicsolvents present in the composition for the formation of the debondinglayer. The composition may be dried by any suitable technique known inthe art. Specifically, the composition may be dried at a temperature of140° C. or below.

The curing may be performed by heat treatment at a temperature of atleast 200° C. or a temperature of 250° C. to 500° C. This heat treatmentmay also be performed in multiple stages at various temperatures withinthe temperature range defined above.

The curing time is not particularly limited and may be, for example, inthe range of 3 to 30 minutes.

After the curing, heat treatment may be optionally further performed.

The subsequent heat treatment is preferably performed at a temperatureof at least 300° C. for 1 to 30 minutes. The heat treatment may beperformed only once. Alternatively, the heat treatment may be performedtwice or more in multiple stages. For example, the heat treatment may beperformed in three stages: first heat treatment at 200 to 250° C.,second heat treatment at 300 to 350° C., and third heat treatment at 400to 450° C.

In step 2, a flexible substrate 13 is formed on the debonding layer 12to produce the laminate.

The flexible substrate 13 is the same as that described above. Theflexible substrate 13 may have a multilayer structure consisting of athin film glass layer 13 a and a polymer layer 13 b. The polymer layer13 b may be provided in plurality. In this case, the polymer layers 13 bmay be formed on both surfaces of the thin film glass layer 13 a. Theflexible substrate 13 may be formed by any suitable method known in theart.

For example, the flexible substrate 13 may have a bilayer structure inwhich the polymer layer 13 b including a polyimide resin is formed underthe thin film glass layer 13 a. In this case, the flexible substrate 13may be formed by applying a composition including a polyamic acid resinto the debonding layer 12, curing the composition by heating at atemperature of 200° C. or above to form the polymer layer 13 b,disposing the thin film glass layer 13 a on the polymer layer 13 b, andheat treating the resulting structure at a temperature of 20 to 300° C.for lamination. Alternatively, a composition including a polyamide resinmay be used instead of the composition including a polyamic acid resin.In this case, the polymer layer 13 b may be formed by drying thecomposition including a polyamide resin.

As an alternative, the flexible substrate 13 may have a trilayerstructure in which the polymer layers 13 b including a polyimide resinare formed on and under the thin film glass layer 13 a. In this case,the flexible substrate 13 may be formed by sequentially forming thefirst polymer layer 13 b including a polyimide resin on the debondinglayer 12, forming the thin film glass layer 13 a on the first polymerlayer 13 b, and forming the second polymer layer 13 b including apolyimide resin on the thin film glass layer 13 a.

Compositions for the formation of the polymer layers may further includeat least one additive commonly used in the art. Examples of suchadditives include binders, solvents, cross-linkers, initiators,dispersants, plasticizers, viscosity modifiers, UV absorbers,photosensitive monomers, and sensitizers.

The curing may also be performed in multiple stages at varioustemperatures within the temperature range defined above.

In the laminate thus produced, the debonding layer exhibits anappropriate adhesive strength to the flexible substrate and can thusproperly fix and support the flexible substrate in a subsequent processfor the fabrication of a device. Accordingly, the use of the laminateaccording to this embodiment of the present invention facilitates theproduction of a substrate of a device (e.g., a flexible display device)including the flexible substrate. In addition, a process for thefabrication of a device can be appropriately carried out on the laminateeven without the need for laser or light irradiation for the separationof the flexible substrate, to fabricate a device with excellentcharacteristics. As a result, the fabrication process of the devicehaving the flexible substrate can be simplified and the fabrication costcan also be reduced.

A further embodiment of the present invention provides a devicesubstrate produced using the laminate and a method for producing thedevice substrate.

The device substrate may be produced by a method including the followingsteps: forming a debonding layer including a polyimide resin on at leastone surface of a carrier substrate; forming a flexible substrate on thedebonding layer; and applying a physical stimulus to the flexiblesubstrate to separate the flexible substrate from the debonding layerformed on the carrier substrate. The steps of forming the debondinglayer and the flexible substrate are the same as those described above.

FIG. 3 a is a schematic view illustrating a process for the productionof a device substrate according to one embodiment of the presentinvention. FIG. 3 a is merely illustrative and the invention is notlimited thereto.

Referring to FIG. 3 a, the device substrate of the present invention maybe produced by a method including the following steps: (S1) forming adebonding layer including a polyimide resin on at least one surface of acarrier substrate; (S2) forming a flexible substrate on the debondinglayer; and (S3 and S4) applying a physical stimulus p to the flexiblesubstrate and separating the flexible substrate from the carriersubstrate on which the debonding layer is formed. The flexible substratemay be separated by a general method used in the art. For example, asuction method may be used to separate the flexible substrate but thepresent invention is not limited thereto. Any method may be selectedthat requires a much smaller force than conventional methods to minimizedamage to a display device during fabrication.

The steps prior to the step of separating the flexible substrate in themethod for producing the device substrate may be the same as those ofthe method for producing the laminate.

The flexible substrate may be separated by applying a suitable physicalstimulus such as cutting, laser cutting or diamond scribing.Specifically, a physical stimulus not greater than 0.1 N may be appliedto separate the flexible substrate.

The device substrate produced by the method includes the flexiblesubstrate separated from the carrier substrate by the application of arelatively small physical stimulus such as cutting even without the needfor further processing such as laser or light irradiation. Accordingly,the use of device substrate can prevent a device from deterioration ofreliability or occurrence of defects caused by laser or lightirradiation. This ensures improved characteristics of the device.

A further embodiment of the present invention provides a deviceincluding the device substrate.

Specifically, the device may be a flexible display device such as asolar cell having a flexible substrate (for example, a flexible solarcell), an organic light emitting diode (OLED) lighting device (forexample, a flexible OLED lighting device), a semiconductor device havinga flexible substrate, an organic electroluminescent device, anelectrophoresis device, or an LCD device. An organic electroluminescentdevice is particularly preferred.

As illustrated in FIG. 3 b, the device may be fabricated by a methodincluding the following steps: sequentially forming a debonding layer 12including a polyimide resin and a flexible substrate 13 on at least onesurface of a carrier substrate 11 to obtain a laminate; forming a devicestructure 30 on the flexible substrate 13 of the laminate (i.e. the stepof fabricating a device); and applying a physical stimulus p withoutlaser or light irradiation to separate the flexible substrate 13 onwhich the device structure 30 is formed.

The device structure may vary depending on the kind of the device to befabricated on the flexible substrate. The device structure may be ageneral one, for example, a semiconductor device structure including agate electrode, a display device structure including a thin filmtransistor array, a diode device structure having a P/N junction, anOLED structure including an organic light emitting layer, or a solarcell structure. As an example, the device structure may be an organicelectroluminescent device structure including: a transparent electrodedisposed at the back side of the flexible substrate and including, forexample, indium tin oxide (ITO); a light emitting part disposed at theback side of the transparent electrode and including, for example, anorganic compound; and a metal electrode disposed at the back side of thelight emitting part and including, for example, a metal.

As described above, the device of the present invention includes, as asubstrate, the flexible substrate separated from the carrier substrateby the application of a physical stimulus without the need for furtherprocessing such as laser or light irradiation. The use of the flexiblesubstrate can ensure improved characteristics of the device and can makethe device highly reliable.

Hereinafter, embodiments of the present invention will be explained indetail such that the invention can be easily carried out by a personhaving ordinary knowledge in the art. The invention may, however, beembodied in many different forms and should not be construed as beinglimited to the embodiments set forth herein.

EXAMPLE 1 Production of Laminate

1 mol of BPDA was polymerized with 0.99 mol of PDA to prepare a polyamicacid resin. A composition including 3 wt % of the polyamic acid resinand 97 wt % of DMAc as a solvent was applied to one surface ofnon-alkali glass as a carrier substrate such that the thickness afterdrying was 0.1 μm. The resulting coating was continuously dried at atemperature of 120° C. and cured at a temperature of 250° C. (for 30min) to form a debonding layer including a polyimide resin (hereinafter,referred to as a ‘first polyimide resin’).

Subsequently, 1 mol of BPDA was polymerized with 0.99 mol of TFMB toprepare a polyamic acid resin. A composition including 12 wt % of thepolyamic acid resin and 88 wt % of DMAc as a solvent was applied (cast)to the debonding layer such that the thickness after drying was 15 μm.The resulting coating was continuously dried at a temperature of 100° C.and cured at a temperature of 350° C. for 60 min to form a polymer layerincluding a polyimide resin (hereinafter, referred to as a ‘secondpolyimide resin’). The resulting laminate (test laminate 1-1) had astructure in which the carrier substrate, the debonding layer includingthe BPDA-PDA polyimide resin, and the polymer layer including theBPDA-TFMB polyimide resin as a flexible substrate were sequentiallydisposed.

Production of Test Laminates

Test laminates were produced in the same manner as in Example 1, exceptthat the kinds of the first polyimide resin for the debonding layer andthe second polyimide resin for the polymer layer of the flexiblesubstrate were changed as shown in Table 3.

TABLE 3 Test laminate No. First polyimide resin Second polyimide resin1-1 BPDA-PDA BPDA-TFMB 1-2 BPDA-PDA BPDA-mPDA 1-3 BPDA-TFMB BPDA-TFMB1-4 BPDA-TFMB BPDA-mPDA 1-5 (Comparative) PMDA-ODA BPDA-TFMB

In Table 3, BPDA represents biphenyl-tetracarboxylic dianhydride, PDArepresents p-phenylenediamine, TFMB represents2,2′-bis(trifluoromethyl)benzidine, mPDA represents m-phenylenediamine,PMDA represents pyromellitic dianhydride, and ODA represents4,4′-oxydianiline.

TEST EXAMPLE 1 Evaluation of Physical Properties of the Debonding Layers

The debonding layers of the test laminates were measured for density,coefficient of thermal expansion (CTE), glass transition temperature(Tg), adhesive strength, and peel strength.

Specifically, the adhesive strength was determined by measuring theforce required to peel the flexible substrate of each laminate from thedebonding layer using a tape without the application of a physicalstimulus (without cutting). The peel strength was determined by cuttingeach laminate into a rectangular shape having a width of 10 mm and alength of 100 mm and measuring the force required when the ends of theflexible substrate were peeled at a rate of 50 mm/min, using a textureanalyzer (TA.XT plus, Stable micro systems). The results are shown inTable 4.

TABLE 4 Physical properties of first Second Test First polyimide Secondpolyimide polyimide resin polyimide resin Adhesive Peel laminate resin(Curing resin (Curing Density CTE Tg CTE strength strength No. temp.:250° C.) temp.: 350° C.) (g/cm³) (ppm/° C.) (° C.) (ppm/° C.) (N/cm)(N/cm) 1-1 BPDA-PDA BPDA-TFMB 1.488 3.590 374 8.205 3.64 0.022 1-2BPDA-PDA BPDA-mPDA 1.488 3.590 374 29.61 3.59 0.029 1-3 BPDA-TFMBBPDA-TFMB 1.475 8.205 352 8.205 3.61 0.132 1-4 BPDA-TFMB BPDA-mPDA 1.4758.205 352 29.61 3.82 0.167 1-5 PMDA-ODA BPDA-TFMB — 20.3 330 8.205 3.771.02 (Comparative) In the table, “—” means “not measured”.

From the results in Table 4, the test laminates 1-1 to 1-4, each ofwhich included the debonding layer including the polyimide preparedusing the tetracarboxylic dianhydride of Formula 1 and the diaminecompound having a linear structure, showed much lower peel strengthsthan the test laminate 1-5 including the polyimide prepared using thetetracarboxylic dianhydride in which the aromatic rings are connectedthrough a linking group.

On the other hand, despite the absence of a linker structure between thearomatic rings, the test laminates 1-3 and 1-4 showed higher peelstrengths than the test laminates 1-1 and 1-2. The reason for the higherpeel strength of each of the test laminates 1-3 and 1-4 is because thetrifluoromethyl group lowered the packing density of the debondinglayer, resulting in higher adhesive strength between the debonding layerand the flexible substrate. However, the test laminates 1-3 and 1-4showed much lower peel strengths than the test laminate 1-5 using thediamine including a linker structure between the aromatic rings.

Changes in the dimension of the test laminates 1-1 and 1-5 with varyingtemperatures were observed, and the results are shown in FIG. 4. As canbe seen from FIG. 4, the test laminate 1-5 underwent a sharp dimensionalchange at around 350° C., unlike the test laminate 1-1.

TEST EXAMPLE 2 Evaluation of Adhesive Strength and Peel StrengthDepending on Curing Temperature

Laminates were produced in the same manner as in Example 1, except thatdebonding layers were formed by curing at various temperatures shown inTable 5.

The adhesive strengths and peel strengths of the flexible substratesdepending on the curing temperatures for the formation of the debondinglayers of the laminates were measured by the same methods as describedin Test Example 1.

After storage of the laminates at 25° C./RH 55% for 1 day, changes inadhesive strength before the application of a physical stimulus wereobserved and changes in peel strength after cutting was performed as aphysical stimulus were observed. The results are shown in Table 5.

TABLE 5 Curing Adhesive Peel temperature strength strength Day (° C.)(N/cm) (N/cm) 0 day 200 3.4 0.24 (immediately after 250 3.64 0.022production) 300 3.68 0.032 1 day 200 3.76 0.24 (after storage at 2503.63 0.024 25° C./RH 55%) 300 3.62 0.036

As shown in the above table, the application of the physical stimulusled to a marked decrease in peel strength. This decrease was morepronounced above a predetermined curing temperature (250° C.).

The adhesive strengths and peel strengths were observed for the laminateof Example 1 having undergone curing at 250° C. immediately afterproduction and after storage at 25° C/RH 55% for 7 days. The results areshown in Table 6.

TABLE 6 Day Adhesive strength (N/cm) Peel strength (N/cm) 0 day 3.640.022 7 days 3.66 0.020

As shown in the above table, the application of the physical stimulusled to a decrease in peel strength. The adhesive strength increased withtime. The peel strength decreased with time but its decrease was notsignificant.

TEST EXAMPLE 3 Evaluation of Peel Strength Depending on the Thickness ofFlexible Substrate

Test laminates were produced in the same manner as in Example 1, exceptthat the kind of the first and second polyimide resins and the thicknessof the flexible substrate were changed as shown in Table 7.

TABLE 7 Debonding layer Flexible substrate Test First Curing SecondCuring Thick- laminate polyimide temper- polyimide temper- ness No.resin ature resin ature (μm) 3-1 BPDA-PDA 250° C. BPDA-TFMB 350° C. 19.73-2 5.2 3-3 2.5 3-4 1.7 3-5 0.9 3-6 BPDA-PDA 450° C. 19 3-7 5.3 3-8 2.13-9 1.4

Peel strengths were measured on the test laminates by the same method asdescribed in Test Example 1. The results are shown in Table 8 and FIG.5.

In Table 8, BPDA-TFMB as the second polyimide resin for the flexiblesubstrates is a transparent polyimide resin and BPDA-PDA as the secondpolyimide resin for the flexible substrates is a colored polyimideresin.

TABLE 8 Second polyimide Thickness of Test resin for flexible AdhesivePeel laminate flexible substrate strength strength No. substrates (μm)(N/cm) (N/cm) 3-1 BPDA-TFMB 19.7 3.88 0.04 3-2 5.2 3.86 0.056 3-3 2.53.52 0.08 3-4 1.7 3.77 0.104 3-5 0.9 3.64 0.136 3-6 BPDA-PDA 19 3.590.072 3-7 5.3 3.67 0.1 3-8 2.1 3.71 0.348 3-9 1.4 3.66 0.428

As can be seen from the test results, as the thickness of each flexiblesubstrate decreased, the peel strength increased. The test laminatesincluding colored BPDA-PDA as the polyimide resin underwent significantchanges in peel strength depending on the thickness of the flexiblesubstrate compared to the test laminates including transparent BPDA-TFMBas the polyimide resin.

TEST EXAMPLE 4 Evaluation of Peel Strength of the Debonding LayersDepending on Curing Conditions

Test laminates were produced in the same manner as in Example 1, exceptthat the curing temperature and time for the formation of the debondinglayer were changed as shown in Table 9.

The test laminates 4-1 to 4-10 were measured for peel strength by thesame methods as described in Test Example 1. The results are shown inTable 9.

TABLE 9 Flexible Debonding layer substrate First Cur- Cur- Second Cur-Test poly- ing ing poly- ing Adhesive Peel laminate imide temp. timeimide temp. strength strength No. resin (° C.) (min) resin (° C.) (N/cm)(N/cm) 4-1 BPDA- 230 3 BPDA- 350 3.56 0.464 4-2 PDA 5 TFMB 3.61 0.0844-3 10 3.44 0.028 4-4 20 3.58 0.03 4-5 30 3.72 0.026 4-6 250 3 3.660.026 4-7 5 3.61 0.0296 4-8 10 3.45 0.0232 4-9 20 3.58 0.0224 4-10 303.64 0.022 Compar- — — — BPDA- 350 3.42 0.524 ative TFMB laminate

As can be seen from the test results, the laminate having undergonecuring at the relatively low temperature for a short time showed peelstrengths similar to the laminate using no first polyimide resin but thelaminates having undergone curing at the same temperature for a longertime showed lower peel strengths than the laminate using no firstpolyimide resin. The laminates having undergone curing at the relativelyhigh temperature showed no substantial difference in peel strengthdepending on the curing time. The laminates having undergone curing atthe relatively high temperature for a short time showed low peelstrengths.

TEST EXAMPLE 5 Evaluation of Peel Strength Depending on the Kind of theFirst Polyimide Resin

Test laminates were produced in the same manner as in Example 1, exceptthat the kind of the first polyimide resin for the formation of thedebonding layer and the kind of the second polyimide resin for theformation of the flexible substrate were changed as shown in Table 10.

TABLE 10 Debonding layer Flexible substrate Curing conditions: 250°Curing conditions: 350° C., 30 min C., 60 min Test First CTE Second CTElaminate polyimide (ppm/ polyimide (ppm/ No. resin ° C.) resin ° C.) 5-1BPDA-PDA 3.590 BPDA-TFMB 8.205 5-2 BPDA-BZD 4.116 5-3 BPDA-mTOL 4.3575-4 ODPA-TFMB 28.09 (Comparative) In the above table, BZD and mTOLrepresent benzidine and m-tolidine, respectively.

The test laminates were measured for adhesive strength and peel strengthby the same methods as described in Test Example 1. The results areshown in Table 11.

TABLE 11 First polyimide Adhe- Test resin for Second polyimide sive Peellaminate debonding resin for strength strength No. layer flexiblesubstrate (N/cm) (N/cm) 5-1 BPDA-PDA BPDA-TFMB 3.64 0.022 5-2 BPDA-BZD3.66 0.0672 5-3 BPDA-mTOL 3.48 0.068 5-4 ODPA-TFMB 3.52 1.23(Comparative)

The reason why the test laminate 5-4 had a very higher peel strengththan the other test laminates is believed to be because the diamine forthe first polyimide resin of the debonding layer includes a linkerstructure between the aromatic rings. The presence of the linkerstructure leads to a low packing density and an increase inintermolecular space. Therefore, the interpenetration of the moleculesis facilitated, resulting in high bonding strength.

The measured peel strength values obtained when BPDA-TFMB was used asthe second polyimide resin for the flexible substrate were compared withthe similarity scores calculated by Equation 1. The results are shown inTable 12.

TABLE 12 First polyimide Peel strength Evalu- MC-based resin value(N/cm) ation similarity score BPDA-PDA 0.022 A 0.3206 BPDA-BZD 0.0672 A0.1675 BPDA-mTOL 0.068 A 0.1917 BPDA-TFMB 0.132 A 0.4291 PMDA-PDA 0.052A 0.2992 BPDA-mPDA Impossible to peel NA 0.5069 PMDA-ODA 1.02 NA 0.6598ODPA-TFMB 1.23 NA 0.5552 A: Accepted, NA: not accepted

As can be seen from the results in Table 12, preferred peel strengthswere obtained when the similarity score was not greater than 0.5.

Test laminates were produced in the same manner as in Example 1, exceptthat heat treatment was performed on a hot plate at 300° C. for 30 minafter curing of the debonding layer. The curing and heat treatmentconditions are shown in Table 13. For the test laminates 5-5, 5-6 and5-7, the heat treatment was repeated 1, 3, and 5 times, respectively.

TABLE 13 Number Debonding layer Flexible substrate of heat Test FirstCuring Second Curing treatments laminate polyimide condi- polyimidecondi- after No. resin tions resin tions curing 5-5 BPDA-PDA 250°BPDA-TFMB 350° 1 C., 30 C., 60 min min 5-6 ″ 250° ″ 350° 3 C., 30 C., 60min min 5-7 ″ 250° ″ 350° 5 C., 30 C., 60 min min

Changes in peel strength according to the number of heat treatmentsafter curing of the debonding layers were observed on the testlaminates. The peel strengths were measured by the same method asdescribed in Test Example 1. The results are shown in Table 14 and FIG.6.

TABLE 14 Test Number Adhesive Peel laminate of heat strength strengthNo. treatments (N/cm) (N/cm) 5-5 1 3.75 0.0210 5-6 3 3.63 0.0210 5-7 53.81 0.0203

As shown in the above table, there were no significant changes in peelstrength despite the increased number of heat treatments after formationof the debonding layers.

TEST EXAMPLE 6 Evaluation of Physical Properties of Polyimide Resins

Polyimide resins usable for the formation of debonding layers andpolymer layers of flexible substrates in the present invention wereevaluated for physical properties.

The tetracarboxylic dianhydride and the diamine compounds shown in Table15 were prepared. 1 mol of the tetracarboxylic dianhydride waspolymerized with 0.99 mol of one of the diamine compounds to prepare apolyamic acid resin. A composition including 12 wt % of the polyamicacid resin and 88 wt % of DMAc as a solvent was applied to one surfaceof non-alkali glass as a carrier substrate such that the thickness afterdrying was 10-15 μm. The resulting coating was continuously dried at atemperature of 120° C. and cured at a temperature of 350° C. to form apolyimide resin layer.

The imidization degree and glass transition temperature (Tg) of thepolyimide resin of the polyimide resin layer were measured. Thecoefficient of thermal expansion (CTE) and 1% thermal decompositiontemperature (Td1%) of the polyimide resin layer including the polyimideresin were measured.

Specifically, the imidization degree was measured by the followingprocedure. First, the composition including the polyamic acid resinprepared by polymerization of the monomers shown in Table 15 wasapplied. Then, the composition was subjected to imidization attemperatures of 200° C. or above and 500° C. or above. The imidizationdegree was defined as the percentage of the integrated intensity of theCN bands observed at 1350 to 1400 cm⁻¹ or 1550 to 1650 cm⁻¹ in the IRspectrum after imidization of the composition at a temperature of 200°C. or above with respect to the integrated intensity (100%) of the CNbands observed in the same wavelength range after imidization of thecomposition at a temperature of 500° C. or above.

The glass transition temperature was measured using a differentialscanning calorimeter (DSC 2010, TA instrument) while heating at a rateof 10° C./min.

The 1% thermal decomposition temperature (Td1%) was determined bymeasuring the temperature at which the initial weight of the polyimidefilm was reduced by 1% while heating at a rate of 10° C./min under anitrogen atmosphere, using a thermogravimetric analyzer (TG-DTA2000).

The coefficient of thermal expansion (CTE) was determined as an averageof the coefficients of linear thermal expansion of the polyimide film asa test piece growing at a load 5 g/film thickness 15 μm and a rate of 5°C./min in the temperature range of 100-200° C. The coefficients oflinear thermal expansion were measured using a thermomechanical analyzer(TMA4000). The results are shown in Table 15.

TABLE 15 Polyimide Imidization CTE Tg Td1% resin degree (ppm/° C.) (°C.) (° C.) BPDA-PDA 95.7 3.590 374 547 BPDA-TFMB 96.2 8.205 352 524

TEST EXAMPLE 7 Changes in Peel Strength Depending on Curing Temperature

Test laminates were produced in the same manner as in Example 1, exceptthat PMDA-PDA was used as the first polyimide resin for debondinglayers, BPDA-PDA was used as the second polyimide resin for flexiblesubstrates, and the curing temperature was changed as shown in Table 16.The test laminates were measured for adhesive strength and peelstrength. The results are shown in Table 16.

TABLE 16 Curing temperature Curing temperature (° C.) of first (° C.) ofsecond Adhe- Test polyimide resin polyimide resin sive Peel laminate(PMDA-PDA) for (BPDA-PDA) for strength strength No. debonding layerflexible substrate (N/cm) (N/cm) 7-1 300 450 3.61 0.09095 7-2 350 4503.55 0.0802 7-3 400 450 3.54 0.0883

TEST EXAMPLE 8 Evaluation of Peel Strength Depending on CopolymerizationMolar Ratio for the Preparation of Polyimide for the Formation ofDebonding Layer

Test laminates were produced in the same manner as in Example 1, exceptthat BPDA and PMDA were used as acid dianhydrides in different molarratios for the formation of debonding layers. The second polyimide forthe formation of flexible substrates was prepared using cyclohexanetetracarboxylic dianhydride (BPDA_H) as an acid dianhydride and4-amino-N-(4-aminophenyl)benzamide (DABA) and 4,4′-diaminodiphenyl ether(ODA) as diamine compounds in a molar ratio of 9:1. The test laminateswere measured for adhesive strength and peel strength. The results areshown in Table 17.

TABLE 17 Test First polyimide resin for Second polyimide resin forAdhesive Peel laminate debonding layer (curing CTE flexible substrate(curing CTE strength strength No. temperature: 300° C.) (ppm/° C.)temperature: 350° C.) (ppm/° C.) (N/cm) (N/cm) 8-1 BPDA7-PMDA3-PDA 3.280BPDA_H-DABA-ODA 52.82 3.59 0.134 8-2 BPDA5-PMDA5-PDA 2.771 3.64 0.0978-3 BPDA3-PMDA7-PDA 2.335 3.66 0.064

TEST EXAMPLE 9 Evaluation of Peel Strength Depending on the Kind ofFlexible Substrate

Two debonding layers were formed in the same manner as in Test Example8. A polyimide for the formation of a flexible substrate was prepared byreacting cyclohexane tetracarboxylic dianhydride (BPDA_H) as an aciddianhydride with 4-amino-N-(4-aminophenyl)benzamide (DABA) andm-phenylenediamine (mPDA) as diamine compounds in a molar ratio of 9:1.One of the debonding layers and the flexible substrate were used toproduce a laminate 9-1. A polyimide for the formation of a flexiblesubstrate was prepared by reacting4,4′-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA) andpyromellitic dianhydride (PMDA) as acid dianhydrides in a molar ratio of1:1 with para-phenylenediamine (PDA). The other debonding layer and theflexible substrate were used to produce a laminate 9-2. The laminateswere measured for adhesive strength and peel strength. The results areshown in Table 18.

TABLE 18 Test First polyimide resin for Second polyimide resin forAdhesive Peel laminate debonding layer (curing CTE flexible substrate(curing CTE strength strength No. temperature: 300° C.) (ppm/° C.)temperature: 350° C.) (ppm/° C.) (N/cm) (N/cm) 9-1 BPDA3-PMDA7-PDA 2.335BPDA_H-DABA-mPDA 44.96 3.58 0.114 9-2 BPDA3-PMDA7-PDA 2.3356FDA-PMDA-PDA 3.926 3.7 0.022

TEST EXAMPLE 10 Evaluation of Peel Strength Depending on BPDA Content ofDebonding Layer

Test laminates were produced to have the compositions shown in Table 19.The adhesive strengths and peel strengths of the debonding layers wereevaluated. It was confirmed that the debonding layers showed lower peelstrengths with increasing PMDA content.

TABLE 19 Test First polyimide resin for Second polyimide resin forAdhesive Peel laminate debonding layer (curing CTE flexible substrate(curing CTE strength strength No. temperature: 300° C.) (ppm/° C.)temperature: 350° C.) (ppm/° C.) (N/cm) (N/cm) 10-1 BPDA3-PMDA7-PDA2.335 BPDA_H-DABA-mPDA 44.96 3.58 0.114 10-2 BPDA2-PMDA8-PDA 1.920 3.660.092 10-3 BPDA1-PMDA9-PDA 1.581 3.56 0.074 10-4 PMDA-PDA 1.348 3.640.052 10-5 — — 3.55 0.737 (Comparative)

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that suchdetailed descriptions are merely preferred embodiments and the scope ofthe present invention is not limited thereto. Therefore, the true scopeof the present invention should be defined by the appended claims andtheir equivalents.

EXPLANATION OF REFERENCE NUMERALS

10, 20 Laminates

11, 21 Carrier substrates

12, 22 Debonding layers

13, 23 Flexible substrates

13 a, 23 a Thin film glass layers

13 b, 23 b, 23 c Polymer layers

30 Device structure

1. A laminate comprising: a carrier substrate; a debonding layerdisposed on at least one surface of the carrier substrate and comprisinga polyimide resin; and a flexible substrate disposed on the debondinglayer, wherein the adhesive strength of the debonding layer to theflexible substrate changes when a physical stimulus causing no chemicalchanges in the debonding layer is applied to the laminate.
 2. Thelaminate according to claim 1, wherein when the adhesive strengths ofthe debonding layer to the flexible substrate before and after thephysical stimulus is applied are defined as A1 and A2, respectively, theratio A2/A1 is from 0.001 to 0.5.
 3. The laminate according to claim 1,wherein the debonding layer has a peel strength not greater than 0.3N/cm from the flexible substrate after the physical stimulus is applied.4. The laminate according to claim 1, wherein the debonding layer has anadhesive strength of at least 1 N/cm to the flexible substrate beforethe physical stimulus is applied.
 5. The laminate according to claim 1,wherein the physical stimulus is applied such that the cross-sections ofthe laminate are exposed.
 6. The laminate according to claim 1, whereinthe polyimide resin has a similarity score not greater than 0.5, ascalculated by Equation 1:Similarity score=α_(FIT)(k ₁ ×Ls _(dianhydride,i) +k ₂ ×Ls_(diamine,j))^(k) ₀   [Equation 1] whereLs_(dianhydride,i)=Exp[−k₃×Coeff_(i)]×V_(i) ^(y) ₀Ls_(diamine,j)=Exp[−k₄×Coeff_(j)]×V_(j) ^(y) ₀ k₀=2.00, y₀=−1.00,k₁=206.67, k₂=124.78, k₃=3.20, k₄=5.90, Coeff_(i) and Coeff_(j) aremolecular asphericities calculated from the structures of dianhydride iand diamine j as monomers of the polyimide, respectively, usingADRIANA.Code (Molecular Networks GmbH), V_(i) and V_(j) are McGowanvolumes calculated from the structures of dianhydride i and diamine j asthe monomers, respectively, using ADRIANA.Code (Molecular NetworksGmbH), and α_(FIT) is 1.0 if exp(−4.0×|Coeff_(i)−Coeff_(j)|)+0.08<0.90and is a constant from 0.1 to 0.95 ifexp(−4.0×Coeff_(i)−Coeff_(j)|)+0.08≧0.90.
 7. The laminate according toclaim 1, wherein the polyimide resin has an imidization degree of 60% to99% when the imidization degree is defined as the percentage of theintegrated intensity of the CN bands observed at 1350 to 1400 cm⁻¹ or1550 to 1650 cm⁻¹ in the IR spectrum after a composition comprising apolyamic acid resin is applied and imidized at a temperature of 200° C.or above with respect to the integrated intensity (100%) of the CN bandsobserved in the same wavelength range after the composition is imidizedat a temperature of 500° C. or above.
 8. The laminate according to claim1, wherein the polyimide resin has a glass transition temperature of200° C. or above.
 9. The laminate according to claim 1, wherein thepolyimide resin is prepared by reacting a tetracarboxylic dianhydride ofFormula 1:

wherein A is a tetravalent aromatic organic group of Formula 2a or 2b:

wherein R₁₁ is a C₁-C₄ alkyl or C₁-C₄ haloalkyl group, a is an integerfrom 0 to 3, and b is an integer from 0 to 2,

wherein R₁₂ to R₁₄ are each independently a C₁-C₄ alkyl or C₁-C₄haloalkyl group, c and e are each independently an integer from 0 to 3,d is an integer from 0 to 4, and f is an integer from 0 to 3, with anaromatic diamine compound having a linear structure to prepare apolyamic acid, and curing the polyamic acid at a temperature of 200° C.or above.
 10. The laminate according to claim 9, wherein the aromaticdiamine compound is represented by Formula 4a or 4b:

wherein R₂₁ is a C₁-C₁₀ alkyl or C₁-C₁₀ haloalkyl group and 1 is aninteger from 0 to 4,

wherein R₂₂ and R₂₃ are each independently a C₁-C₁₀ alkyl or C₁-C₁₀haloalkyl group, X is selected from the group consisting of —O—,—CR₂₄R₂₅—, —C(═O)—, —C(═O)O—, —C(═O)NH—, —S—, —SO—, —SO₂—,—O[CH₂CH₂O]_(q)—, C₆-C₁₈ monocyclic and polycyclic cycloalkylene groups,C₆-C₁₈ monocyclic and polycyclic arylene groups, and combinationsthereof, R₂₄ and R₂₅ are each independently selected from the groupconsisting of a hydrogen atom, C₁-C₁₀ alkyl groups, and C₁-C₁₀ haloalkylgroups, q is an integer of 1 or 2, m and n are each independently aninteger from 0 to 4, and p is an integer of 0 or
 1. 11. The laminateaccording to claim 1, wherein the debonding layer is formed by applyinga composition comprising the polyimide resin or a precursor thereof tothe carrier substrate and curing the composition at a temperature of200° C. or above.
 12. The laminate according to claim 1, wherein thedebonding layer has a coefficient of thermal expansion not higher than30 ppm/° C. at a temperature of 100 to 200° C. and a 1% thermaldecomposition temperature (Td1%) of 450° C. or above.
 13. The laminateaccording to claim 1, wherein the debonding layer has a thickness of0.05 to 5 μm.
 14. The laminate according to claim 1, wherein theflexible substrate has a structure selected from the group consisting ofa thin film glass layer, a polymer layer, and a multilayer laminatethereof.
 15. The laminate according to claim 14, wherein the polymerlayer comprises at least one polymer resin selected from the groupconsisting of polyethersulfone, polyethylene naphthalate, polyethyleneterephthalate, polycarbonate, polyimide, polyether imide, polyamideimide, polyester, polyether amide imide, polyester amide imide, andpolyarylate.
 16. The laminate according to claim 14, wherein the polymerlayer comprises a polyimide resin having an imidization degree of 50 to99% and a glass transition temperature of 200° C. or above.
 17. A methodfor producing a laminate, comprising: forming a debonding layercomprising a polyimide resin on at least one surface of a carriersubstrate; and forming a flexible substrate on the debonding layer,wherein the debonding layer is formed by applying a compositioncomprising the polyimide resin or a precursor thereof to the carriersubstrate and curing the composition at a temperature of 200° C. orabove.
 18. The method according to claim 17, wherein the flexiblesubstrate is formed by a method selected from the group consisting of amethod comprising disposing a glass thin film layer on the debondinglayer and heat treating the glass thin film layer at a temperature of 20to 300° C., a method comprising applying a composition comprising apolymer or a precursor thereof and curing the composition, and acombination thereof.
 19. The method according to claim 17, furthercomprising heat treating the debonding layer at a temperature of 300° C.or above for 1 to 30 minutes after the step of forming the debondinglayer.
 20. A method for producing a device substrate, comprising:producing a laminate comprising a carrier substrate, a debonding layer,and a flexible substrate by the method according to claim 17; applying aphysical stimulus to the laminate without causing chemical changes inthe debonding layer; and separating the flexible substrate from thecarrier substrate on which the debonding layer is formed.
 21. The methodaccording to claim 20, wherein the physical stimulus is applied suchthat the cross-sections of the laminate are exposed.
 22. A devicesubstrate produced by the method according to claim
 20. 23. A method forfabricating a device, comprising: producing a laminate comprising acarrier substrate, a debonding layer, and a flexible substrate by themethod according to claim 17; forming a device structure on the flexiblesubstrate of the laminate; and applying a physical stimulus to thelaminate on which the device structure is formed, without causingchemical changes in the debonding layer, and separating the flexiblesubstrate on which the device structure is formed, from the debondinglayer of the laminate.
 24. A device fabricated by the method accordingto claim
 23. 25. The device according to claim 24, wherein the device isselected from the group consisting of solar cells, organic lightemitting diode lighting devices, semiconductor devices, and displaydevices.
 26. The device according to claim 25, wherein the displaydevices are flexible organic electroluminescent devices.